Copying from NAS to External

I need to move a folder from my Network Drive (Iomega Home Media Drive) to an external HD to backup 100 gb worth of data. I am running Mac osx 10.6. I tried dragging and dropping the folder from the NAS to the External HD and I always get an error during the copying process that says "The operation can not be completed because an item name "(Folder name)" already exists". After checking google it looks like it may be a bug in finder and that I could use terminal to copy the items, but I do not know how to copy from the NAS drive. If I use the Terminal command "cp -r [source folder] [destination directory]/[foldername]/" and my NAS drive is the source folder what would I need to type for [source folder]?

Thanks in advance,

Bobby